Interelectrode capacitance:

Any 2 pieces of conducting material, when they are brought closer to each other, will behave as a capacitor. Often, this interelectrode capacitance is so small that it can even be neglected. It hardly amounts to more than a few picofarads.

In alternating current circuits and at the audio frequencies, interelectrode capacitance is not significant. But it can cause problems at the radio frequencies. The chances for the trouble increase as frequency increases. The common phenomena are feedback, and the change in frequency characteristics of the circuit.

Interelectrode capacitance is minimized by keeping the wire leads as short as possible. It is reduced by using shielded cables and by enclosing circuits in metal housings if the interaction might produce trouble. This is why, if you have ever opened up the sophisticated communications radio, you may have seen sevearl metal enclosures inside main box.